In my earlier U.S. Pat. No. 4,343,607, issued Aug. 10, 1982, I described a spray system for a kilned lumber pile breakdown hoist.
More of the background and a brief summary of the prior invention now patented in U.S. Pat. No. 4,343,607 are contained in Griffin, "Combustor Adapted to Direct Fire Kilns", Timber Processing Industry, Aug. 1980, front cover and pp 10-12 and 14.
Until shortly prior to the filing of the U.S. patent application which matured as U.S. Pat. No. 4,343,607, as is stated in the specification of that patent, it was the almost unexceptional practice to dry lumber after sawing, using the burning of fossil fuel, particularly natural gas to create the necessary heated-gas stream for circulation through the kiln. Various proposals had been made and tried for direct-fired combustors using wood waste, particularly sawdust, as fuel, but incompleteness of combustion has always represented a difficult problem. Lately, as the cost of petroleum has risen, the desire to switch to sawdust as fuel for heating the lumber kiln gas stream has become irresistible. Fortunately, there have been a number of improvements made in combustors in recent years, e.g. the development of fluidized-bed combustion techniques, so that it is now reasonable to burn sawdust, or a mixed fuel largely consisting of sawdust, to produce the heated dry gas stream for kilning lumber.
One unavoidable product of the combustion of sawdust is ash: fine particulate material consisting of that which would not or did not burn completely and that which when burned remained or produced a solid. Under most operating conditions, the great bulk of the ash will fail to become entrained in the heated gas stream, and if so-entrained, will be removed in the bag house filters or the multiclone filters on the upstream side of the kiln. However, a certain amount of the particulates cannot be removed by the filters and will be carried through the kiln in the heated gas stream. Some of this will silt-out within the kiln and will deposit on the lumber being kilned.
Typically, within a modern lumber kiln, a multi-course pile of lumber is subjected as a unit to the heated gas stream. In order to ensure even and thorough treatment the various courses are stacked with the aid of spacing courses--each being an open layer comprising a few sticks placed crosswise to the direction of the lengths of lumber in the immediately subjacent and superjacent courses.
Accordingly, as the stacked lumber is being kilned in a direct-fired sawdust fueled combustor, one can expect the pile of lumber exiting the kiln to bear a deposit of fine ash not just on the outer, upper or exposed lengths in the pile, but throughout the pile, potentially on every piece in each course.
A piece of apparatus has been developed and become widely used for converting the pile of kilned lumber into a single layer of uniformly oriented lengths for further processing, e.g. for planing. One type of such controlled destacking apparatus is known as a breakdown hoist.
At a breakdown hoist, one lateral side of the pile of kilned lumber is supported using a weir-like wall means along the full height of the pile and then the pile and wall are tilted so that all courses are supported against this wall. Next the wall is gradually lowered relative to the tilted stack so that support is serially withdrawn from first the upper course of lumber, then from the layer of spacer sticks which immediately underlaid that layer, and so on. Usually, this relative lowering is effected by raising the stack relative to the wall, so that the site where the layers become unsupported remains stationary. Immediately downstream of the site where the uppermost layer of lumber in the tilted pile becomes exposed on its downward-tilted side, there is provided a feeding deck, which may take the form of an inclined set of rails or the like leading down to a conveyor. Usually, this conveyor is the feed conveyor for a further processing station, e.g. a planer mill. A provision is generally made so that each layer of the spacer sticks as it becomes exposed falls down between the tilted stack and the feeding deck, and each layer of kilned lumber as it becomes exposed tumbles down the incline and onto the feed conveyor.
Where an ash-producing direct fired combustor has been used to kiln the lumber, this operation of destacking by tilting, sliding and tumbling is accompanied by the billowing-up of clouds of ash as it is violently shaken-free of the kilned lumber and spacer sticks. And that which remains on and around the lumber entering the planer mill acts as an abrasive on the moving and cutting parts, so that the bearings, planer knives and the like become worn and dull at an excessive rate.
According to my aforesaid prior patented invention, the ash was kept from becoming an airborne irritant, by spraying the upper face of the pile as it was being destacked, with sufficient water to wet-down the ash. As to each course in the pile, the wetting down was completed before that course slid or tumbled from the pile onto the feeding deck.
When the aforesaid earlier invention was made, the usual practice was to run the kilned rough lumber through a planer mill and possibly through other downstream finishing operations while it remained exteriorly wetted by the spray. In the course of conducting these finishing operations, a substantial portion of the wetted superficial portion of the lumber was cut or worn away, and due to the frictional heat generated in the finishing process, much of the rest of the moisture which had soaked into the lumber simply evaporated. To the extent that the finished lumber was still damp, it could be stacked with spacers and dried or permitted to dry.
While the invention works very well when the lumber is to be finished according to the process just outlined, in recent times, what has grown to be a substantial portion of the kilned lumber is not going to be immediately completely finished following destacking onto the feeding deck. Instead, much of it is to be sorted, graded, cut to length if necessary, and packaged for shipment, most frequently for export by ship. Often this lumber is not to be planed in the course of its transit from the feeding deck to the packaging station. Accordingly, if the lumber were wetted-down as it was destacked onto the feeding deck, it would remain wet at the packaging station. If packaged wet, the lumber would be prone to suffer excessive mildew and mold damage during shipment.
Accordingly, I have rethought my prior invention and have devised a way to abate the kiln ash problem without substantially wetting the lumber, and at a cost comparable to that of establishing and running the process of my prior invention.